E. coli is a Gram-negative, short rod-shaped bacterium belonging to the genus Escherichia and the family Enterobacteriaceae, and is found as part of the normal flora in the intestines of various animals including mammals. It was revealed that most strains of E. coli are non-pathogenic and can cause opportunistic infections, but some highly pathogenic strains cause diverse intestinal diseases and sepsis in mammals including humans. Of them, strains causing gastrointestinal diseases can be largely classified into six groups based on their virulence, Enterotoxigenic E. coli (ETEC), Enteropathogenic E. coli (EPEC), Enterohemorrhagic E. coli (EHEC), Enteroaggregative E. coli (EAEC), Enteroinvasive E. coli (EIEC), and Necrotoxigenic E. coli (NTEC). Enterotoxigenic E. coli (ETEC) is known to be associated with infections in pigs. In general, diseases caused by bacterial or viral infections can be diagnosed by identification of the pathogens. However, since E. coli is present in the intestines of healthy animals, early diagnosis of diseases caused by E. coli infections is difficult (Korean Patent No. 963157).
ETEC is a Gram-negative rod-shaped bacterium, and either motile with peritrichous flagella or non-motile without flagella. ETEC is an aerobic or facultative anaerobic bacterium producing acid and gas from lactose and fructose, and grows well on common media at a temperature between 7-48° C., temperature being optimal at 35-37° C., and at pH 4.5-9.0. ETEC produces a toxin similar to the cholera toxin, and this toxin can be divided into a heat-labile enterotoxin (LT) losing its activity when heated at 60° C. for 10 minutes and a heat-stable enterotoxin showing a resistance after heated at 100° C. for 30 minutes. When infected, cholera-like symptoms are shown, and it proliferates in the upper part of the small intestine and the bacterial concentration reaches 107-108 cfu (colony formation unit) per ml, leading to occurrence of E. coli infectious diseases.
Recently, in light of the trend toward large-scale corporate swine production, colibacillosis in pigs has become a common and frequent emerging problem in piggeries (Park Young-il, Sun-Jin Publishing Co. 353-359, 1998). In Korea, the recent increasing occurrence of swine colibacillosis has been causing growth retardation and death of young pigs due to diarrhea, resulting in tremendous economic losses to farmers (Hong Eu-Chul, master's thesis, Dankook University, Addition Effect of Egg Yolk in Early Weaned Piglets, 2001). Many antibiotics have been used for the prevention and treatment of swine colibacillosis, but the misuse and overuse of antibiotics have given rise to the serious problems of drug resistance and drug residues in pigs. Thus, the use of antibiotics has been restricted in many countries worldwide (Mason H S et al., Trends in Biotech. 13:388-392, 1995).
Meanwhile, bacteriophage is a specialized type of virus that infects only particular bacteria and controls the growth of bacteria, and can self-replicate only inside host bacteria. Bacteriophage consists of genetic material in the form of single or double stranded DNA or RNA. Based on their morphology, bacteriophages are divided into Myoviridae, Siphoviridae, and Podoviridae, which are characterized by contractile, long non-contractile, and short tails, respectively (Arch Virol (2001) 146:843-857; Elizabeth Kutter et al., Bacteriophages Biology and Application; CRC press).
After the discovery of bacteriophages, a great deal of effort was initially placed in using them for infectious-disease therapy. However, compared to antibiotics having broad target spectrum, bacteriophages were seen as unnecessary due to having a specific target spectrum. Nevertheless, the misuse and overuse of antibiotics resulted in rising concerns about antibiotic resistant bacteria and harmful effects of residual antibiotics in foods (Cislo, M et al. Arch Immunol. Ther. Exp. 1987.2:175-183; Kim sunghun et al., bacteriophage, New Alternative Antibiotics. BRIC).
These growing concerns have led to a resurgence of interest in bacteriophage. Seven bacteriophages for control of E. coli 0157:H are disclosed in U.S. Pat. No. 6,485,902 (2002) and two bacteriophages for control of various microorganisms are disclosed in U.S. Pat. No. 6,942,858 (issued to Nymox in 2005).